Micro electro-mechanical systems (MEMS) devices are devices that combine mechanical elements and electronic elements on a common substrate. MEMS devices are used in a wide variety of electronic devices. For example, many projectors employ a type of MEMS device known as a digital micromirror device (DMD). A DMD has a large number of very small mirrors that can be individually controlled to modulate light in accordance with image data, to assist in projecting a corresponding image on a screen.
A packaged semiconductor device that includes a MEMS device typically includes a substrate, such as a lead frame, on which the MEMS device is mounted. The MEMS device is usually electrically connected to the substrate using wire-bonding technology. Specifically, a ball bond is formed between a wire and a bonding pad of the MEMS device, a reverse-motion loop is created in the wire, and then another bond is formed between the wire and a bonding pad of the substrate. The reverse-motion loop in the wire may be needed to ensure the integrity and reliability of the wire bond.
The MEMS device itself includes a relatively thick upper portion, or lid, that maintains a sufficient pressure difference with the outside atmosphere so that the device properly functions. However, the thickness of the lid makes it difficult to form a proper wire bond between the MEMS device and the substrate. Specifically, the thickness of the lid makes it difficult to form the reverse-motion loop in the wire, without placing bond pads on the device further from the edge of the lid, which increases the cost of the device.